The parvovirus replicative form DNA is being used as a probe for the analysis of eukaryotic DNA replication. The mechanism of replication of replicative form DNA is being studied to determine the role of cellular and viral proteins using biochemical and genetic methods. Conditional lethal mutants are being isolated and nonsense and deletion mutants will be constructed in vitro. Recombinant DNA techniques will be used to advance these studies and to attempt the cloning of a cell replication origin for the construction of an autonomously replicating DNA vector derived from the linear parvovirus replicon.